Implementation, development and evaluation of the gas-phase chemistry within the Global/Regional NMMB/BSC Chemical Transport Model (NMMB/BSC-CTM)

Air pollution is a serious issue that affects human health, the environment and the climate at levels from local to global scales. The main processes that affect air pollution levels are: emissions, chemistry, transport and deposition. Air quality models (AQMs) are mathematical tools that describe relevant physicochemical processes and quantify concentrations of air pollutants. Therefore, AQMs can be used to develop and detail measures taken to reduce air quality problems. Several AQMs are currently used and they have undergone a rapid evolution in recent years. Computer capacity has increased during the last decade enabling us to use higher spatial resolutions and more complex parameterizations schemes that resolve more complex atmospheric processes. Moreover, previous research has shown that the feedbacks between meteorology and chemistry are important in the context of many research applications. Therefore, this increase in computing power allows accurately simulate those feedbacks (online modelling). Online models are becoming more used in the atmospheric community. The NMMB/BSC Chemical Transport Model (NMMB/BSC-CTM) is being developed through an ongoing team effort at the Earth Sciences Department of the Barcelona Supercomputing Center (BSC). The main motivation for this thesis is to contribute in the development of a unified fully coupled chemical weather prediction system able to solve gas-aerosol-meteorology interactions within a wide range of scales on local to global domains that can be used in both operational and research applications. In this sense, the focus in this Ph.D. has been on the development and evaluation of the tropospheric gas-phase chemistry within the online Global / Regional atmospheric model NMMB/BSC-CTM. With the meteorological core NMMB as the starting point, different parameterizations of several atmospheric chemistry processes such as dry deposition, photolysis, wet deposition, gas-phase chemistry, and stratospheric ozone handling have been reviewed, implemented and evaluated during this Ph.D. thesis. A complete spatial, temporal and vertical model evaluation of the relevant chemical species using different observational data has been performed in this Ph.D. thesis. Observational data has included ground-monitoring stations, ozonesondes, satellite data, climatologies and, aircraft campaigns. This is the first time that the gas-phase chemistry of the NMMB/BSC-CTM has been evaluated on a regional and global scales over a full year. Concerning the model evaluation in the regional scale, we had the opportunity to participate in the Air Quality Model Evaluation International Initiative (AQMEII) Phase2 which aims to intercompare online coupled regional-scale models over North America and Europe. In this sense, we were participating in this initiative in the European runs with NMMB/BSC-CTM model. The model evaluations have shown a good agreement with observations. Overall, the model performance corresponds to state-of-the-art regional and global AQMs.La contaminació de l’aire és un problema greu que afecta la salut humana i el medi ambient, tant a escala local com global. Els principals processos que concerneixen els nivells de contaminació de l’aire són les emissions, la química, el transport i la deposició. Els Models de Qualitat de l’Aire (AQMS) són eines matemàtiques que descriuen aquests processos fisicoquímics i quantifiquen les concentracions de contaminants de l’aire. Per tant, els AQMS es poden utilitzar per desenvolupar i detallar les mesures preses per reduir la mala qualitat de l’aire. Actualment, es fan servir diversos AQMS i aquests darrers anys han evolucionat molt ràpidament. La capacitat de la computació ha augmentat durant l’última dècada, i això ha fet possible una resolució espacial més bona i uns esquemes de parametritzacions més complexos que resolen més processos atmosfèrics. D’una altra banda, la investigació ha demostrat que els feedbacks entre la meteorologia i la química són certament importants en moltes aplicacions de recerca. Per tant, l’augment de la potència de càlcul permet simular acuradament aquests feedbacks (modelizació online). Els models online són cada vegada més utilitzats en la comunitat atmosfèrica. El NMMB/BSC Chemical Transport Model (NMMB/BSC-CTM) es desenvolupa gràcies a un esforç d’equip al Departament de Ciències de la Terra del Barcelona Supercomputing Center (BSC). La principal motivació d’aquesta tesi és contribuir al desenvolupament i a l’avaluació d’un sistema de predicció unificat que sigui capaç de resoldre les interaccions gas-aerosolmeteorologia dins un ampli rang d’escales, des de dominis locals a globals, i que pugui ser utilitzat tant en aplicacions operatives com d’investigació. En aquest sentit, el principal objectiu d’aquesta tesi doctoral és el desenvolupament i l’avaluació de la química troposfèrica en fase gasosa del model online global/regional NMMB/BSC-CTM. Utilitzant el nucli meteorològic NMMB com a punt de partida, diverses parametritzacions de processos químics atmosfèrics com ara la deposició seca, la fotòlisi, la química dels núvol, la química en fase gasosa i l’intercanvi d’ozó entre estratosfera i troposfera han estat revisats, implementats i avaluats durant aquesta tesi doctoral. S’ha dut a terme una avaluació completa a nivell espacial, temporal i vertical de les espècies químiques més rellevants mitjançant diverses observacions a escala global i regional. Aquestes observacions inclouen estacions a nivell de superfície, ozonosondes, dades de satèl.lit, climatologies i campanyes d’aeronaus. És la primera vegada que la química en fase gasosa de l’NMMB/BSC-CTM s’avalua a escala global i regional durant un any complet. Respecte l’evaluació del model a nivell regional, vam tenir l’oportunitat de participar en el projecte de l’Air Quality Model Evaluation International Initiative (AQMEII) Phase2. L’objectiu principal d’aquest projecte és la intercomparació de models online a escala regional sobre l’Amèrica del Nord i Europa. El nostre grup va participar en aquesta iniciativa sobre el domini europeu utilitzant el model NMMB/BSC-CTM. L’avaluació del model mostra una bona avinença amb les observacions. En general, els resultats del model es corresponen amb l’estat de l’art dels AQMS a escala regional i global.Postprint (published version

On discrete maximum principles for discontinuous Galerkin methods

The aim of this work is to propose a monotonicity-preserving method for discontinuous Galerkin (dG) approximations of convection–diffusion problems. To do so, a novel definition of discrete maximum principle (DMP) is proposed using the discrete variational setting of the problem, and we show that the fulfilment of this DMP implies that the minimum/maximum (depending on the sign of the forcing term) is on the boundary for multidimensional problems. Then, an artificial viscosity (AV) technique is designed for convection-dominant problems that satisfies the above mentioned DMP. The noncomplete stabilized interior penalty dG method is proved to fulfil the DMP property for the one-dimensional linear case when adding such AV with certain parameters. The benchmarks for the constant values to satisfy the DMP are calculated and tested in the numerical experiments section. Finally, the method is applied to different test problems in one and two dimensions to show its performance

Shock capturing techniques for hp-adaptive finite elements

The aim of this work is to propose an hp-adaptive algorithm for discontinuous Galerkin methods that is capable to detect the discontinuities and sharp layers and avoid the spurious oscillation of the solution around them. In order to control the spurious oscillations, artificial viscosity is used with the particularity that it is only applied around the layers where the solution changes abruptly. To do so, a novel troubled-cell detector has been developed in order to mark the elements around those layers and to impose linear order in them. The detector takes advantage of the evolution of the value of the gradient through the adaptive process.Peer ReviewedPostprint (published version

Differentiable monotonicity-preserving schemes for discontinuous Galerkin methods on arbitrary meshes

This work is devoted to the design of interior penalty discontinuous Galerkin (dG) schemes that preserve maximum principles at the discrete level for the steady transport and convection–diffusion problems and the respective transient problems with implicit time integration. Monotonic schemes that combine explicit time stepping with dG space discretization are very common, but the design of such schemes for implicit time stepping is rare, and it had only been attained so far for 1D problems. The proposed scheme is based on a piecewise linear dG discretization supplemented with an artificial diffusion that linearly depends on a shock detector that identifies the troublesome areas. In order to define the new shock detector, we have introduced the concept of discrete local extrema. The diffusion operator is a graph-Laplacian, instead of the more common finite element discretization of the Laplacian operator, which is essential to keep monotonicity on general meshes and in multi-dimension. The resulting nonlinear stabilization is non-smooth and nonlinear solvers can fail to converge. As a result, we propose a smoothed (twice differentiable) version of the nonlinear stabilization, which allows us to use Newton with line search nonlinear solvers and dramatically improve nonlinear convergence. A theoretical numerical analysis of the proposed schemes shows that they satisfy the desired monotonicity properties. Further, the resulting operator is Lipschitz continuous and there exists at least one solution of the discrete problem, even in the non-smooth version. We provide a set of numerical results to support our findings

On discrete maximum principles for discontinuous Galerkin methods

The aim of this work is to propose a monotonicity-preserving method for discontinuous Galerkin (dG) approximations of convection–diffusion problems. To do so, a novel definition of discrete maximum principle (DMP) is proposed using the discrete variational setting of the problem, and we show that the fulfilment of this DMP implies that the minimum/maximum (depending on the sign of the forcing term) is on the boundary for multidimensional problems. Then, an artificial viscosity (AV) technique is designed for convection-dominant problems that satisfies the above mentioned DMP. The noncomplete stabilized interior penalty dG method is proved to fulfil the DMP property for the one-dimensional linear case when adding such AV with certain parameters. The benchmarks for the constant values to satisfy the DMP are calculated and tested in the numerical experiments section. Finally, the method is applied to different test problems in one and two dimensions to show its performance.Preprin

Sensitivity study of PBL schemes and soil initialization using the WRF-BEP-BEM model over a Mediterranean coastal city

Altres ajuts: acords transformatius de la UABUnidad de excelencia María de Maeztu CEX2019-000940-MDue to increased urbanization and global warming, cities are experiencing more heat wave (HW) events that cause extreme heat stress. To mitigate such effects, a better understanding of the impact of urban morphology on the boundary layer development is needed. This study investigates the sensitivity of mesoscale simulations using the WRF model coupled with the building effect parameterization and the building energy model (BEP-BEM) at a 1-km resolution to 1) soil moisture initializations; 2) the inclusion of site-specific urban morphology parameters; and 3) the planetary boundary layer (PBL) scheme. A HW episode that occurred in the metropolitan area of Barcelona serves as the case study. We find that the use of a high-resolution land data assimilation system (HRLDAS) to initialize soil properties results in larger temperature diurnal range, but it did not improve the performance of simulated temperatures compared to using low-resolution ERA5 data. The inclusion of site-specific urban parameters improved the representation of urban fractions, reducing the night-time overprediction of 2-m temperatures compared to using default urban parameters. Overall, the Bougeault-Lacarrere (BouLac) scheme represents the PBL-height noontime observations better than the Mellor-Yamada-Janjic (MYJ) scheme. This was related to a better representation of daytime near-surface temperatures by the BouLac scheme compared to the MYJ schem

Modelling the impacts of emission changes on O3 sensitivity, atmospheric oxidation capacity and pollution transport over the Catalonia region

oai:publications.copernicus.org:egusphere109352Tropospheric ozone (O3) is an important surface pollutant in urban areas, and it has complex formation mechanisms that depend on the atmospheric chemistry and meteorological factors. The severe reductions observed in anthropogenic emissions during the COVID-19 pandemic can further our understanding of the photochemical mechanisms leading to O3 formation and provide guidance for policies aimed at reducing air pollution. In this study, we use the air quality model WRF-Chem coupled with the urban canopy model BEP-BEM to investigate changes in the ozone chemistry over the Metropolitan Area of Barcelona (AMB) and its atmospheric plume moving northwards, which is responsible for the highest number of hourly O3 exceedances in Spain. The trajectories of the air masses from the AMB to the Pyrenees are studied with the Lagrangian particle dispersion model FLEXPART-WRF. The aim is to investigate the response of ozone chemistry to changes in the precursor emissions. The results show that with the reduction in emissions: 1) the ozone chemistry tends to enter the nitrogen oxide (NOx)-limited or transition regimes; however, highly polluted urban areas are still in the Volatile Organic Compounds (VOC)-limited regime, 2) the reduced O3 production is overwhelmed by reduced nitric oxide (NO) titration, resulting in a net increase in the O3 concentration (up to 20 %) in the evening, 3) the increase in the maximum O3 level (up to 6 %) during the lockdown could be attributable to an enhancement in the atmospheric oxidation capacity (AOC), 4) the daily maximum levels of ozone and odd oxygen species (Ox) generally decreased (4 %) in May with the reduced AOC, indicating an improvement in the air quality, and, 5) ozone precursor concentration changes in the AMB contribute to the pollution plume moving along the S&ndash;N valley to the Pyrenees. Our results indicate that O3 abatement strategies cannot rely only on NOx emission control but must include a significant reduction in anthropogenic sources of VOCs (e.g., for power plants and heavy industry). In addition, our results show that mitigation strategies intended to reduce O3 should be designed according to the local meteorology, air transport, particular ozone regimes and AOC of the urban area.</p

Gas-phase chemistry in the online multiscale NMMB/BSC Chemical Transport Model: Description and evaluation at global scale

This paper presents a comprehensive description and benchmark evaluation of the tropospheric gas-phase chemistry component of the NMMB/BSC Chemical Transport Model (NMMB/BSC-CTM), an online chemical weather prediction system conceived for both the regional and the global scale. We provide an extensive evaluation of a global annual cycle simulation using a variety of background surface stations (EMEP, WDCGG and CASTNET), ozonesondes (WOUDC, CMD and SHADOZ), aircraft data (MOZAIC and several campaigns), and satellite observations (SCIAMACHY and MOPITT). We also include an extensive discussion of our results in comparison to other state-of-the-art models. The model shows a realistic oxidative capacity across the globe. The seasonal cycle for CO is fairly well represented at different locations (correlations around 0.3–0.7 in surface concentrations), although concentrations are underestimated in spring and winter in the Northern Hemisphere, and are overestimated throughout the year at 800 and 500 hPa in the Southern Hemisphere. Nitrogen species are well represented in almost all locations, particularly NO2 in Europe (RMSE below 9 μg m−3). The modeled vertical distribution of NOx and HNO3 are in excellent agreement with the observed values and the spatial and seasonal trends of tropospheric NO2 columns correspond well to observations from SCIAMACHY, capturing the highly polluted areas and the biomass burning cycle throughout the year. Over Asia, the model underestimates NOx from March to August probably due to an underestimation of NOx emissions in the region. Overall, the comparison of the modelled CO and NO2 with MOPITT and SCIAMACHY observations emphasizes the need for more accurate emission rates from anthropogenic and biomass burning sources (i.e., specification of temporal variability). The resulting ozone (O3) burden (348 Tg) lies within the range of other state-of-the-art global atmospheric chemistry models. The model generally captures the spatial and seasonal trends of background surface O3 and its vertical distribution. However, the model tends to overestimate O3 throughout the troposphere in several stations. This is attributed to an overestimation of CO concentration over the southern hemisphere leading to an excessive production of O3. Overall, O3 correlations range between 0.6 to 0.8 for daily mean values. The overall performance of the NMMB/BSC-CTM is comparable to that of other state-of-the-art global chemical transport models.The authors wish to thank WOUDC, GAW, EMEP, WDCGG, CASTNET-EPA, NADP and EANET for the provision of measurement stations. Also, thanks go to the free use of the MOPITT CO data obtained from the NASA Langley Research Center Atmospheric Science Data Center. SCIAMACHY radiances have been provided by ESA. This work is funded by grants CGL2013-46736-R, Supercomputación and e-ciencia Project (CSD2007-0050) from the Consolider-Ingenio 2010 program of the Spanish Ministry of Economy and Competitiveness. Further support was provided by the SEV-2011-00067 grant of the Severo Ochoa Program, awarded by the Spanish Government. A.H. received funding from the Earth System Science Research School (ESSReS), an initiative of the Helmholtz Association of German research centres (HGF) at the AlfredWegener Institute for Polar and Marine Research. All the numerical simulations were performed with the MareNostrum Supercomputer hosted by the Barcelona Supercomputing Center. We also thank Beatriz Monge-Sanz for providing the COPCAT coefficients.Peer ReviewedPostprint (author's final draft

Abating heat waves in a coastal Mediterranean city : What can cool roofs and vegetation contribute?

Unidad de excelencia María de Maeztu CEX2019-000940-MAltres ajuts: Acord transformatiu CRUE-CSICThe frequency and intensity of heat waves (HW) in cities are on the rise due to climate change as well as urban fabric materials and anthropogenic activities that affect heat accumulation. The efficacy of HW mitigation strategies depends on a city's specific and unique morphology, land use, building materials, climate and geography. In this study, we show the effectiveness of cool roofs and vegetation in reducing temperature in the Metropolitan Area of Barcelona (AMB). We use the Weather and Research Forecasting (WRF) model with the urban scheme BEP+BEM, including11 urban classes to simulate a HW that occurred in August 2015. We find that cool roofs reduce temperature best during the day (0.67 °C average and 2.22 °C maximum reductions), while additional green areas moderate temperatures to a lesser degree but also more evenly during the day and at night (average reductions of 0.15 °C and 0.17 °C, respectively). However, when irrigation is increased, the temperature reduction during the day is intensified due to the cooling effect of more evapotranspiration. The thermal regulation of combining the two strategies is the most evenly distributed over the AMB and has the highest impact, with an average and maximum reduction of 1.26 °C and 4.73 °C at 13:00UTC

A take-home message from COVID-19 on urban air pollution reduction through mobility limitations and teleworking

Unidad de excelencia María de Maeztu CEX2019-000940-MThe rigorous traffic limitations during COVID-19 have forced many people to work from home, reaching an outstanding degree of teleworking and reduction in air pollution. This exceptional situation can be examined as a large-scale pilot test to determine the potential of improving urban air quality through teleworking. Based on observed traffic reductions during the COVID-19 lockdown in Barcelona, we formulate socio-occupational scenarios, with various configurations of teleworking, and simulate them using the chemistry transport model WRF-Chem with multi-layer urban scheme. By intensifying teleworking to 2, 3, and 4 days a week, averaged NO2 concentrations are reduced by 4% (−1.5 μg m−3), 8% (−3 μg m−3), and 10% (−6 μg m−3), respectively, while O3 increases moderately (up to 3 μg m−3). We propose that teleworking be prioritized and promoted as an effective contribution towards reduction of long-term urban air pollution and short-term pollution peaks